SEM inspection and analysis of patterned photoresist features

ABSTRACT

A process for improving the accuracy of critical dimension measurements of features patterned on a photoresist layer using a scanning electron microscope (SEM) is disclosed herein. The process includes providing an electron beam to the photoresist layer and transforming the surface of the photoresist layer before the SEM inspection. The surface of the photoresist layer is transformed to trap the outgassing volatile species and dissipates built up charge in the photoresist layer, resulting in SEM images without poor image contrast.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. application Ser. No.09/819,342 by Shields et al., entitled “Process for FormingSub-Lithographic Photoresist Features by Modification of the PhotoresistSurface;” U.S. application Ser. No. 09/819,692 by Okoroanyanwu et al.,entitled “Process for Preventing Deformation of Patterned PhotoresistFeatures by Electron Beam Stabilization;” U.S. application Ser. No.09/819,344 by Okoroanyanwu et al., entitled “Process for Reducing theCritical Dimensions of Integrated Circuit Device Features;” U.S.application Ser. No. 09/819,343 by Gabriel et al., entitled “SelectivePhotoresist Hardening to Facilitate Lateral Trimming;” and U.S.application Ser. No. 09/819,552 by Gabriel et al., entitled “Process forImproving the Etch Stability of Ultra-Thin Photoresist,” all filed on aneven date herewith and assigned to the Assignee of the presentapplication.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuits (ICs).More particularly, the present application relates to a method andapparatus for improved scanning electron microscope (SEM) inspection andanalysis of patterned photoresist features utilized to fabricate ICs.

BACKGROUND OF THE INVENTION

During integrated circuit (IC) fabrication, various surfaces involvedtherein are inspected and analyzed for a variety of reasons. Forexample, the dimensions of features provided on a given surface may bemeasured and/or their alignment with respect to other features may beanalyzed. Features provided on a given surface may be inspected foruniformity, integrity and/or defects. A semiconductor substrate,photoresist feature, or a layer above the semiconductor substrate can beinspected.

The semiconductor substrate or a layer above the semiconductorsubstrate, collectively, a semiconductor wafer, may be inspected todetermine whether further processing should continue, whether the wafershould be discarded, or whether an appropriate corrective measure shouldbe taken before further processing of the wafer continues. In thismanner, the likelihood of defects occurring during the IC fabricationprocess can be decreased or eliminated.

Various techniques can be utilized to inspect and analyze the wafer.Optical microscopes, scanning electron microscopes (SEMs), orlaser-based systems may be utilized for inspection and measurementtasks. Some of the tasks require human involvement and others are fullyautomated so that human involvement is unnecessary.

Layers or surfaces which are present on the wafer only during the ICfabrication process (i.e., layers or surfaces which do not comprise theend product IC) are also commonly inspected. For example, layers ofphotoresist material can be inspected following development(after-develop-inspection or “ADI”) to ensure that the pattern transferprocess has been performed correctly and/or that the pattern is withinspecified tolerances. From such inspection, mistakes or unacceptableprocess variations associated with the layer of photoresist material canbe identified and corrected since the layer of photoresist material hasnot yet been utilized to produce any physical changes to the waferitself, such as, by doping, etching, etc. Defective layers ofphotoresist material can be corrected by stripping and reapplying a newlayer of photoresist material on the wafer.

Critical dimensions of patterned features on a layer of photoresistmaterial are commonly measured using an SEM inspection and analysistool. This measurement task involves obtaining SEM images of thepatterned features. The SEM inspection and analysis tool obtains SEMimages of a given sample using an inspection electron beam, theinspection electron beam characterized by a low beam current (on theorder of pA) and an accelerating voltage of approximately 300-1500 V.The sample is rapidly scanned by the inspection electron beam so as toobtain imaging data but not long enough to intentionally affect thesample.

The SEM inspection and analysis tool includes an electron gun, one ormore lens assemblies, and photomultiplier detectors, all within a vacuumenvironment at approximately 10⁻⁷ Torr. Electrons emitted from theelectron gun, i.e., the inspection electron beam, are focused by thelens assemblies to form primary electrons that impinge on a sample to beimaged (e.g., the patterned layer of photoresist material). Theinteraction of the impinging primary electrons with the surface of thesample causes secondary electrons to be emitted from the sample. Thesecondary electrons are generated from the top portion of the sample,within a depth of approximately 50-60 Å from the top surface. Thesesecondary electrons are collected by the photomultiplier detectors andcomprise the imaging data from which SEM images are generated.

However, when the photoresist material is an organic-based photoresistmaterial, SEM images of features patterned thereon are susceptible topoor image contrast, and this in turn may lead to erroneous criticaldimension measurements. SEM images with degraded image contrast arecaused by undesirable interaction of the primary electrons with thesample (e.g., the organic-based photoresist material). Instead of merelycausing secondary electrons to be emitted from the organic-basedphotoresist material, the primary electrons may also cause volatileorganic species to be emitted or outgassed from the organic-basedphotoresist material (i.e., the outgassing problem). These volatileorganic species interact with and scatter the secondary electrons suchthat the secondary electrons that are collected by the photomultiplierdetectors are distorted imaging data representative of the patternedfeatures on the photoresist material. Consequently SEM images generatedtherefrom are less than ideal, such as, suffering from degraded imagecontrast.

Additionally, organic-based photoresist materials have a tendency tobuild up charge and/or heat from the impinging primary electrons (i.e.,the charging and heating problems). Organic-based photoresist materialsexhibit insulative properties and can build up charge and/or beat fromthe beam current of the primary electrons. Because the constituentscomprising the organic-based photoresist material have varyinginsulative properties with respect to each other, charge and/or heatdissipation is also non-uniform and/or insignificant. When excessivecharge and/or heat builds up within the material, structural or physicalchanges can occur such that patterned features may become permanentlydistorted and damaged. Hence, not only are the SEM images inaccurate butsubsequent pattern transfer to underlying layers of the wafer is alsoadversely impacted. As features are lithographically patterned at everdecreasing dimensions, the outgassing, charging, and/or heating problemsassociated with SEM imaging of organic-based photoresist surfaces arebecoming progressively worse.

Thus, there is a need for improved SEM inspection and analysis ofpatterned features on a layer of photoresist material. There is afurther need for a process for reducing charging and/or heating problemsassociated with SEM imaging of organic-based photoresist materials.There is still a further need for a process for reducing undesirableoutgassing problems associated with SEM imaging of organic-basedphotoresist materials.

BRIEF SUMMARY OF THE INVENTION

One exemplary embodiment relates to a method of inspecting a surfaceassociated with manufacture of an integrated circuit. The methodincludes providing an electron beam to the surface, and transforming atleast a portion of the surface. The method further includes inspectingthe surface using a scanning electron microscope (SEM). The transformingstep occurs before the inspecting step.

Another exemplary embodiment relates to a patterned photoresist layer.The layer is configured to facilitate accurate critical dimensionmeasurements of features thereon using a scanning electron microscope(SEM). The layer includes a treated region and an untreated region. Thetreated region comprises a top surface and side surfaces surrounding theuntreated region. The treated region has at least one of a differentelectrical and material property relative to the untreated region.

Still another exemplary embodiment relates to a process for reducing thebuild up of at least one of charge, heat, and volatile species in aphotoresist layer during scanning electron microscope (SEM) inspection.The process includes exposing the photoresist layer to a flood electronbeam, and forming a shell in the photoresist layer in response to theflood electron beam. The photoresist layer includes at least onepatterned feature having a top surface, side surfaces, and an untreatedportion. The shell is comprised of the top surface and the sidesurfaces. The shell reduces the build up of at least one of charge,heat, and volatile species associated with at least one feature duringSEM inspection.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments will become more fully understood from thefollowing detailed description, taken in conjunction with theaccompanying drawings, wherein like reference numerals denote likeelements, in which:

FIG. 1 is a flow diagram showing a process for obtaining accuratecritical dimension measurements in accordance with an exemplaryembodiment;

FIG. 2 is a general schematic block diagram of a lithographic system forpatterning a wafer in accordance with an exemplary embodiment;

FIG. 3 is a cross-sectional view of the wafer illustrated in FIG. 2,showing a developing step;

FIG. 4 is a cross-sectional view of the wafer illustrated in FIG. 3,showing an electron beam exposure step; and

FIG. 5 is a scanning electron microscope (SEM) analysis and inspectiontool in accordance with an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In one embodiment of the present invention, an advantageous process forobtaining accurate critical dimension (CD) measurements of featurespatterned on a photoresist layer during an integrated circuit (IC)fabrication is provided. An exemplary embodiment of the presentinvention will be described with respect to a flow diagram shown in FIG.1. The flow diagram includes a patterning step 40, a developing step 42,an electron beam exposure step 44, a scanning electron microscope (SEM)analysis and inspection step 46, and a critical dimension measurementsstep 48.

Patterning step 40 is carried out using a lithography system 10, asshown in FIG. 2. Lithographic system 10 includes a chamber 12, a lightsource 14, a condenser lens assembly 16, a mask or a reticle 18, anobjective lens assembly 20, and a stage 22. Lithographic system 10 isconfigured to transfer a pattern or image provided on mask or reticle 18to a wafer 24 positioned in lithography system 10. Lithographic system10 may be a lithographic camera or stepper unit. For example,lithographic system 10 may be a PAS 5500/900 series machine manufacturedby ASML, a microscan DUV system manufactured by Silicon Valley Group, oran XLS family microlithography system manufactured by IntegratedSolutions, Inc. of Korea.

Wafer 24 includes a substrate 26, a layer 28, and a photoresist layer30. Photoresist layer 30 is disposed over layer 28, and layer 28 isdisposed over substrate 26. Wafer 24 can be an entire integrated circuit(IC) wafer or a part of an IC wafer. Wafer 24 can be a part of an IC,such as, a memory, a processing unit, an input/output device, etc.Substrate 26 can be a semiconductor substrate, such as, silicon, galliumarsenide, germanium, or other substrate material. Substrate 26 caninclude one or more layers of material and/or features, such as lines,interconnects, vias, doped regions, etc., and can further includedevices, such as, transistors, microactuators, microsensors, capacitors,resistors, diodes, etc.

Layer 28 can be an insulative layer, a conductive layer, a barrierlayer, or other layer of material to be etched, doped, or layered. Inone embodiment, layer 28 can comprise one or more layers of materials,such as, a polysilicon stack comprised of a plurality of alternatinglayers of titanium silicide, tungsten silicide, cobalt silicidematerials, etc. In another embodiment, layer 28 is a hard mask layer,such as, a silicon nitride layer or a metal layer. The hard mask layercan serve as a patterned layer for processing substrate 26 or forprocessing a layer upon substrate 26. In yet another embodiment, layer28 is an anti-reflective coating (ARC). Substrate 26 and layer 28 arenot described in a limiting fashion, and can each comprise a conductive,semiconductive, or insulative material.

Photoresist layer 30 can comprise a variety of photoresist chemicalssuitable for lithographic applications. Photoresist layer 30 is selectedto have photochemical reactions in response to electromagnetic radiationemitted from light source 14. Materials comprising photoresist layer 30can include, among others, a matrix material or resin, a sensitizer orinhibitor, and a solvent. Photoresist layer 30 is preferably achemically amplified, positive or negative tone, organic-basedphotoresist. Photoresist layer 30 may be, but is not limited to, anacrylate-based polymer, an alicyclic-based polymer, or a phenolic-basedpolymer. For example, photoresist layer 30 may comprise PAR700photoresist manufactured by Sumitomo Chemical Company. Photoresist layer30 is deposited, for example, by spin-coating over layer 28. Photoresistlayer 30 is provided at a thickness of less than 1.0 μm.

Chamber 12 of lithographic system 10 can be a vacuum or low pressurechamber for use in ultraviolet (UV), vacuum ultraviolet (VUV), deepultraviolet (DUV), extreme ultraviolet (EUV), x-ray, or other types oflithography. Chamber 12 can contain any of numerous types ofatmospheres, such as, nitrogen, etc. Alternatively, chamber 12 can beconfigured to provide a variety of other patterning scheme.

Light source 14 provides light or electromagnetic radiation throughcondenser lens assembly 16, mask or reticle 18, and objective lensassembly 20 to photoresist layer 30. Light source 14 is an excimerlaser, in one embodiment, having a wavelength of 365 nm, 248 nm, 193 nm,157 nm, or 126 nm, or a soft x-ray source having a wavelength at 13.4nm. Alternatively, light source 14 may be a variety of other lightsources capable of emitting radiation having a wavelength in theultraviolet (UV), vacuum ultraviolet (VUV), deep ultraviolet (DUV),extreme ultraviolet (EUV), x-ray or other wavelength range.

Assemblies 16 and 20 include lenses, mirrors, collimators, beamsplitters, and/or other optical components to suitably focus and directa pattern of radiation (i.e., radiation from light source 14 as modifiedby a pattern or image provided on mask or reticle 18) onto photoresistlayer 30. Stage 22 supports wafer 24 and can move wafer 24 relative toassembly 20.

Mask or reticle 18 is a binary mask in one embodiment. Mask or reticle18 includes a translucent substrate 32 (e.g., glass or quartz) and anopaque or absorbing layer 34 (e.g., chromium or chromium oxide) thereof.Absorbing layer 34 provides a pattern or image associated with a desiredcircuit pattern, features, or devices to be projected onto photoresistlayer 30. Alternatively, mask or reticle 18 may be an attenuating phaseshift mask, an alternating phase shift mask, or other type of mask orreticle.

Utilizing lithographic system 10, the pattern or image on mask orreticle 18 is projected onto and patterned on photoresist layer 30 ofwafer 24. Next, in developing step 42, wafer 24 is exposed to adeveloper, as is well-known in the art, to develop the pattern onphotoresist layer 30. Referring to FIG. 3, a cross-sectional view of aportion of wafer 24 after developing step 42 is shown. The developedpattern includes features 50 and 51.

After photoresist layer 30 has been developed but before featuresthereon are transferred onto any of the underlying layers, such as layer28, electron beam exposure step 44 is performed. Wafer 24 may be removedfrom chamber 12 and placed within a different chamber and/or a differentenvironment which provides electron beam tools. Alternatively, chamber12 may be configured to include additional chambers and/or toolssuitable to perform step 44.

In FIG. 4, there is shown wafer 24 undergoing electron beam exposurestep 44. A flood electron beam 52 impinges on the exposed surfaces ofwafer 24 and chemically transforms or modifies such exposed surfaces toa certain depth. For feature 50, a top surface or region 54 andsidewalls or side regions 56 are transformed into a shell 58. Similarly,for feature 51, a top surface or region 60 and sidewalls or side regions62 are transformed into a shell 64. Hence, upon completion of step 44,feature 50 will comprise an untreated region 66 and shell 58, untreatedregion 66 being encapsulated from underneath by layer 28 and on allother sides or faces by shell 58. Similarly, feature 51 will comprise anuntreated region 68 and shell 64, untreated region 68 being encapsulatedfrom underneath by layer 28 and on all other sides or faces by shell 64.

Electron beam 52 is preferably emitted from an extended area electronsource (not shown) and is a uniform collimated beam that is floodexposed over the entire wafer 24 at a normal angle of incidence. Theextended area electron source is of the cold cathode type and generateselectron beam 52 from the energetic impact of ions against a suitablemetal. An example of an extended area electron source suitable togenerate electron beam 52 is manufactured by Electron VisionCorporation.

The electron beam flood exposure conditions (e.g., beam current, dose,and accelerating voltage) are selected such that layer 30 will not meltand flow, which will cause distortions in features 50, 51. Instead,conditions are selected to cause molecules of layer 30 which interactwith electron beam 52 to undergo a chemical change, i.e., cross-linking,to the extent that the functional groups of the polymer materialcomprising such molecules will become decomposed. Shells 58 and 64 arerepresentative of the decomposed regions of layer 30. The portions offeatures 50, 51 that electron beam 52 are unable to penetrate orbombard, i.e., untreated regions 66, 68, remain unaffected (i.e., thepolymer functional groups of untreated regions 66, 68 are notcross-linked to the point of complete decomposition).

The degree of decomposition that the functional groups of the polymermaterial comprising layer 30 will undergo is a function of the dose ofelectron beam 52. In one embodiment, electron beam 52 is provided at abeam current in the order of approximately 3 mA, a dose in the range ofapproximately 500 to 4000 μC/cm², and preferably, at approximately 2000μC/cm², and an accelerating voltage of approximately 3-5 keV. Theconditions are selected to form shells 58, 64 configured to suitablyaddress the charging and outgassing problems associated with SEManalysis and inspection. Alternatively, when layer 30 comprises othertypes of materials, the beam current and dosage of electron beam 52 maybe selected to cause desirable chemical changes such that the changedportions of layer 30 will facilitate obtaining accurate CD measurements,as will be described in greater detail below.

The penetration depth of electron beam 52 into layer 30 is a function ofthe energy of electron beam 52. The penetration depth also determinesthe depth or thickness of each of shells 58, 64. In one embodiment, thedepth of shells 58, 64 can be selected as a function of the acceleratingvoltage of electron beam 52 and this relationship can be approximatelyexpressed as: $R_{g} = \frac{0.046V_{a}^{1.75}}{d}$

where R_(g) is the penetration depth in microns, V_(a) is theaccelerating voltage or energy in keV, and d is the density of thetarget material (e.g., layer 30) in g/cm³. Preferably, the acceleratingvoltage of electron beam 52 is provided at up to approximately 10 keV.More preferably, the accelerating voltage is in the range ofapproximately 3-5 keV.

In any case, the depth of shells 58, 64 is selected in accordance withthe performance or conditions associated with the SEM analysis andinspection carried out in step 46. In one embodiment, the depth ofshells 58, 64 is in the range of approximately 30 to 200 Å, and morepreferably, is up to 50 to 60 Å thick.

In step 46, SEM images of the patterned features on layer 30 aregenerated using an SEM analysis and inspection tool 100 (FIG. 5), toobtain CD measurements of such patterned features (e.g., to measure thelateral dimensions of features 50 and 51) before they are transferredonto underlying layers (e.g., layer 28) of wafer 24.

Tool 100 includes a chamber 102, an electron gun 104, an opticalassembly 106, detectors 108, a computer or analyzer 110, and a stage112. Although not shown, tool 100 may further include other components,such as, filters, analog-to-digital (A/D) converters, amplifiers,input/output devices, controllers, storage devices, etc.

In one embodiment, chamber 102 is maintained under vacuum at a pressureof approximately 10⁻⁷ Torr. Electrons are emitted from electron gun 104and configured into primary electrons 114 by optical assembly 106.Optical assembly 106 may be one or more lens assemblies, and may includelenses, filters, beam splitters, mirrors, etc., which generate a focusedand collimated primary electrons 114. Primary electrons 114 impinge onwafer 24, and in particular, on layer 30. Tool 100 preferably images aportion of wafer 24 at any given time and as such, wafer 24 may beprovided over stage 112 for translation. Alternatively, wafer 24 may bestationary and tool 100 may move during step 46.

The interaction of primary electrons 114 with layer 30 causes secondaryelectrons (not shown) to be emitted from layer 30. The secondaryelectrons are collected by detectors 108 and electrical signalsrepresentative thereto are communicated to computer 110 for processingand analysis. Although two detectors 108 are shown in FIG. 5, detectors108 may comprise one or more detectors that are suitably positionedrelative to wafer 24 to receive the secondary electrons. Detectors 108can be photomultiplier detectors. Computer 110 utilizes the electricalsignals from detectors 108 to generate SEM images of the surface ofwafer 24, i.e., the patterned features on layer 30. Such SEM images arethen inspected, either by a human operator or through an automatedprocess, to obtain CD measurements associated with the patternedfeatures on layer 30 (e.g., the lateral dimensions of features 50 and51) (step 48).

Ideally, primary electrons 114 should penetrate layer 30 up to a certaindepth and only secondary electrons should be emitted from layer 30.Otherwise, primary electrons 114 should have no other interaction withor impact on wafer 24. In reality, SEM imaging causes, among others, acharge to build up in layer 30 and/or outgassing of volatile speciesfrom layer 30, resulting in SEM images with degraded image contrast andthis, in turn, leading to erroneous CD measurements. Moreover, theheating and charging occurring in layer 30, if severe enough, can causethe patterned features to become permanently distorted. The electronbeam treatment of step 44 advantageously minimizes or eliminates suchproblems.

The cross-linked regions (e.g., shells 58, 64) of layer 30 havedifferent structural or material properties relative to thenon-cross-linked regions (e.g., untreated regions 66, 68) of layer 30.Among others, the cross-linked regions are more dense, less porous, andare harder or stiffer than the none cross-linked regions. When the depthof shells 58, 64 is selected to be equal to or greater than thepenetration depth of primary electrons 114, the secondary electronsemitted from features 50, 51 are predominantly from shells 58, 64 (asopposed to untreated regions 66, 68). Because of the specific propertiesof shells 58, 64, they will not outgas volatile organic species uponinteraction with primary electrons 114. Moreover, since primaryelectrons 114 will have little or no interaction with untreated regions66, 68, outgassing of volatile organic species from untreated regions66, 68 is also minimized or eliminated.

When the depth of shells 58, 64 is selected to be less than thepenetration depth of primary electrons 114, the secondary electrons areemitted from both shells 58, 64 and untreated regions 66, 68 forfeatures 50, 51, respectively. Advantageously, volatile organic specieswhich would otherwise be outgassed from untreated regions 66, 68 intochamber 102 are trapped within layer 30 by shells 58, 64. Hence, shells58, 64 are configured with respect to the operating conditions of tool100 and the characteristics of the material comprising layer 30 (e.g.,an organic-based photoresist material) such that outgassing of volatileorganic species from layer 30 into chamber 102 is prevented by thetrapping or barrier capability of shells 58, 64. If Volatile organicspecies were to escape layer 30, they would interact with and scatterprimary electrons 114, resulting in SEM images with poor contrast andpoor CD measurement accuracy. Examples of volatile organic speciesinclude isobutene, benzylic photoacid generator fragments, etc.

Shells 58, 64 also have different optical and electrical propertiesrelative to untreated regions 66, 68. The constituent material elementscomprising untreated regions 66, 68 (e.g., residual solvent, photoresistadditives, etc.) have different electrical properties relative to eachother which can impede smooth dissipation of the beam current associatedwith SEM imaging, leading to a charge build up in features 50, 51. Incontrast, the electrical and optical properties of shells 58, 64 aremore uniform than those of untreated regions 66, 68. Hence, not only areshells 58, 64 less likely to build up a charge, their uniform orhomogeneous electrical properties also promote smooth dissipation of anybuilt-up charge. This results in SEM images without degraded imagecontrast and also reduces distortions or damage to features 50, 51,which may occur with significant charging and/or heating problems.

It should be understood that SEM tool 100 as shown in FIG. 5 anddescribed herein are for illustration purposes only and are not meant tobe limiting. SEM tool 100 may be configured in a variety of other waysto perform a desired inspection of features patterned on layer 30 afterdevelopment but before pattern transfer to underlying layers.

Once SEM imaging data have been obtained via detectors 108, such dataare analyzed and processed, as is well-known in the art, by computer 110in step 48 to generate CD measurements that actually represent thelateral dimensions of features on layer 30.

In this manner, charging, heating, and/or outgassing problems associatedwith SEM inspection of features patterned on a photoresist layer duringIC fabrication can be significantly reduced or even eliminated. Anelectron beam treatment of the photoresist layer to modify its outersurfaces to a certain depth leads to the formation of a shell or barrierfor each feature patterned on the photoresist layer. These shellsprevent the outgassing of species which may scatter and interact withthe SEM's electron beam and provide a region for smoothly dissipatingbuilt-up charge or heat from the SEM's electron beam. The resulting SEMimages no longer suffer from image contrast problems and ultimately theCD measurements obtained therefrom will be highly accurate. Thepatterned features are also less likely to become permanently distortedor damaged as a consequence of undergoing SEM inspection. In oneembodiment, charging, heating, and/or outgassing problems typicallyassociated with SEM inspection of organic-based photoresist layer may bereduced by 95% or better.

It is understood that although the detailed drawings, specific examples,and particular values describe the exemplary embodiments of the presentinvention, they are for purposes of illustration only. The exemplaryembodiments of the invention are not limited to the precise details anddescriptions described herein. For example, although particularmaterials or chemistries are describes, other materials or chemistriescan be utilized. Various modifications may be made if the detailsdisclosed without departing from the spirit of the invention as definedin the following claims.

What is claimed is:
 1. A method of inspecting a surface associated withmanufacture of an integrated circuit, the method comprising the stepsof: providing an electron beam to the surface; transforming at least aportion of the surface; and inspecting the surface using a scanningelectron microscope (SEM), wherein the transforming step occurs beforethe inspecting step, wherein the surface includes at least one patternedfeature having a top portion, side portions, and a bottom portion, andthe transforming step includes chemically changing the top portion andthe side portions to form a shell that encapsulates the bottom portion.2. The method of claim 1, wherein the electron beam is a flood electronbeam.
 3. The method of claim 2, wherein the shell has a depth in therange of approximately 30 to 200 Å.
 4. The method of claim 2, whereinthe surface is an organic-based photoresist layer.
 5. The method ofclaim 4, wherein the transforming step includes decomposing polymerfunctional groups included in the top and the side portions.
 6. Themethod of claim 1, wherein the inspecting step includes at least one ofpreventing volatile species from leaving the surface and substantiallydissipating a charge built up in the surface.
 7. A patterned photoresistlayer configured to facilitate accurate critical dimension measurementsof features thereon using a scanning electron microscope (SEM), thelayer comprising: a treated region; and an untreated region, wherein thetreated region comprises a top surface and side surfaces surrounding theuntreated region, and the treated region having at least one of adifferent electrical and material property relative to the untreatedregion.
 8. The layer of claim 7, wherein the material comprising thepatterned photoresist layer is an organic-based polymer.
 9. The layer ofclaim 7, wherein the treated region is formed by flood exposing thepatterned photoresist layer to an electron beam.
 10. The layer of claim9, wherein the electron beam has a beam current of approximately 3 mA, adose in the range of approximately 500-4000 μC/cm², and an acceleratingvoltage up to approximately 10 keV.
 11. The layer of claim 9, whereinthe electron beam has a dose of approximately 2000 μC/cm² and anaccelerating voltage in the range of approximately 3-5 keV.
 12. Thelayer of claim 9, wherein the electron beam cross-links and decomposespolymer functional groups included in the material comprising thetreated region.
 13. The layer of claim 7, wherein the treated region hasa thickness of approximately 30 to 200 Å.
 14. The layer of claim 7,wherein the treated region is configured to prevent outgassing speciesgenerated by the untreated region from coming into contact with the SEM.15. The layer of claim 7, wherein the treated region is configured todissipate a charge generated in the patterned photoresist layer inassociation with the use of the SEM.
 16. A process for reducing thebuild up of at least one of charge, heat, and volatile species in aphotoresist layer during scanning electron microscope (SEM) inspection,the process comprising: exposing the photoresist layer to a floodelectron beam, the photoresist layer including at least one patternedfeature having a top surface, side surfaces, and an untreated portion;and forming a shell in the photoresist layer in response to the floodelectron beam, wherein the shell is comprised of the top surface and theside surfaces, and the shell reduces the build up of at least one ofcharge, heat, and volatile species associated with the at least onefeature during SEM inspection.
 17. The process of claim 16, wherein theexposing step includes exposing the flood electron beam having operatingconditions of approximately 3 mA, 500-4000 μC/cm², and up to 10 keV. 18.The process of claim 16, wherein the shell surrounds the untreatedportion and a thickness of the shell is approximately 30-200 Å.
 19. Theprocess of claim 16, wherein the forming step includes cross-linking thetop surface and the side surfaces to form the shell.
 20. The process ofclaim 16, wherein the forming step includes decomposing the functionalgroups included in the top surface and the side surfaces to form theshell.